The present invention relates to a thermally insulated conduit and more particularly, the invention relates to a tube system which is comprised of an inner tube, an outer tube being arranged coaxially to the inner tube, and a spacer construction disposed in between these tubes to hold them in concentric relation while thermally insulating them from each other. The invention relates in particular to the spacer construction and to the assembling of such a coaxial tube or conduit system.
The German printed patent application No. 1,960,932 describes a conduit system of the type referred to above and in which the inner tube is preferably a copper tube while the outer tube has resulted from folding a metal or synthetic ribbon in longitudinal direction around the inner tube. The spacer construction is a paper string helically wound around the inner tube prior to forming the outer tube about the inner tube while any residual space between the tubes has subsequently been filled with a synthetic foam, such as polyurethane. Such a tube assembly is, however, disadvantaged by the fact that the helical spacer impedes the distribution of the foam. This is particularly true when the radial distance between the tubes is rather small. As a consequence, voids have existed in the foam layer which have impeded the strength of the assembly.